This invention relates generally to explosive compositions and intermediate compounds for use in an explosive composition and more specifically to explosive compositions and intermediate compounds derived from glycerol.
Trinitro-based explosives, so-called first generation explosives, for example trinitroglycerine (NG) and trinitrotoluene (TNT), are powerful “high” explosives. However the biggest mark against their use is their relative thermodynamic instability, and their tendency to spontaneously explode, which make these explosives unsafe to handle. What distinguishes these explosives over later generations of explosives is the presence of a fuel and an oxidant on the same molecule i.e. the hydrocarbon skeleton providing the fuel and nitrate moieties providing the oxidant.
Emulsion explosives are a later generation of explosives which are ammonium nitrate (AN) based and are currently widely used in civil applications. These explosives however exhibit relatively slower reaction rates when compared to the aforementioned high explosives.
An emulsion explosive typically comprises an oxidant, a carbonaceous fuel, such as diesel (the AN and fuel oil mixture is termed ANFO), and a surfactant. The oxidant, usually ammonium nitrate (NH4NO3), supplies oxygen atoms to the fuel, usually a hydrocarbon compound, such that the fuel can be oxidized to carbon dioxide (CO2) and water (H2O) in a rapid exothermic reaction.
Emulsion explosives typically comprise a continuous organic or major phase (e.g. the carbonaceous fuel) and a discontinuous aqueous or minor phase containing the oxidant (e.g. AN). With the separation of the oxidant and the fuel in two phases, these explosives are relatively easily handled but this comes at a cost of a relative loss of explosive power.
An advantage to the use of emulsion explosives is that the base emulsion is non detonable. Base emulsion typically has a density greater than 1.3 g/cm3. At this density the emulsion will not detonate. The emulsion needs to be sensitized by the addition of a sensitizing agent such as micro balloons or sodium nitrite. This will reduce the density of the emulsion to around 1.0 g/cm3. During the sensitizing process, small voids are introduced to the emulsion which act as hot spots during initiation, leading to detonation.
Since AN does not dissolve in hydrocarbons but is highly soluble in water, and to provide for a large contact surface between the oxidant and the fuel, the AN solution is emulsified in the hydrocarbon. Emulsification occurs with the introduction of a surfactant (emulsifier), one of several types, and intense stirring. An emulsion explosive can therefore be described as a highly concentrated AN solution dispersed in the hydrocarbon as droplets, having a diameter ranging from 0.01 to 10 μm, with the surfactant in the interface between the hydrocarbon and each AN solution droplet.
A surfactant, in this context, is not only an essential component to an emulsion explosive but it also provides a secondary fuel source in the composition.
It is conventional for surfactants, made for this application, to be manufactured with the aid of emulsifiers based on sugar esters. More recently polyisobutylene succinic anhydride (PIBSA) based surfactants have found increasing use in this application as they generally result in more stable emulsions. Also PIBSA is amenable to processing which allows for the manufacture of a wide range of PIBSA based surfactants, each one engineered for a particular explosive application, especially with regards to shelf life, viscosity and cost.
Whilst emulsion explosives have many advantages in the civil context, several negative economic and environmental factors associated with the component compounds of these explosives, i.e. PIBSA, AN, and carbonaceous fuels, weigh against their use. As PIBSA is manufactured from mineral oils, it is inexorably tied to crude oil, its fluctuating availability and cost. Coupled to this factor are the environmental issues associated with crude oil production. With regards to AN, it is currently in short supply worldwide.
From the aforegoing it is clear that there is a need for an explosive composition which has component compounds which are manufactured from raw and intermediate materials, which are readily and cheaply available, which are relatively easily transported and handled in situ, which have a relatively low environmental impact and which have high explosive power akin to the first generation explosives.
The invention at least partially addresses the aforementioned problems.